Method for aligning mechanical filters

ABSTRACT

In a mechanical filter, the coupling elements coupling the individual filter resonators to each other comprise a material having a Young&#39;&#39;s modulus dependent upon the final heat treatment temperature. In a method for aligning the filter, the coupling elements are subjected to heat treatment, the maximum temperature of which is higher than the final heat treatment temperature.

United States Patent [191 1 Giinther 1 Mar. 19, 1974 METHOD FOR ALIGNINGMECHANICAL FILTERS [75] Inventor: Alfhart Giinther, I-Iaar, Germany [73]Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Germany 22Filed: Sept.24, 1971 21 Appl.No.: 183,423

[52] US. Cl 148/13, 148/127, 148/134, 148/154 [51] Int. Cl. C21d l/00,C22f 1/00 [58] Field of Search 148/13, 127, 134, 154; 75/65 EB [56]References Cited UNITED STATES PATENTS 3,547,713 12/1970 Steinemann etal. 148/13 2,342,274 2/1944 I-Iecht 148/134 3,499,804 3/1970 Clarke3,364,087 l/l968 Solomon et a] 75/65 EB Primary ExaminerRichard 0. DeanAttorney, Agent, or Firm-Herbert L. Lerner [5 7] ABSTRACT In amechanical filter, the coupling elements coupling the individual filterresonators to each other comprise a material having a Youngs modulusdependent upon the final heat treatment temperature. In a method foraligning the filter, the coupling elements are subjected to heattreatment, the maximum temperature of which is higher than the finalheat treatment temperature.

5 Claims, 5 Drawing Figures comm DEVICE PATENTEDMARIQIQM 3,798,077

SHEET 1 OF 3 Fig. 1

Fig. 2

MUDULUS E OF 185 o I 3 o THERMELAST 1 I I I I I I TEMPERATURE TIN CFATENTEDMAR 1 9 T974 3.798.077

sum 2 [IF 3 0,03- RELATIVE CHANGE OF YUUNG'S []I[]2 MUDULUS r i 1 i [00050E] BUU TEMPERATURE TIN C PATENTEDMAR 19 m4 3,798,077

SHEEI 3 [1F 3 EUNTROL DEVICE Fig. 5

@AIGHT SUURCE15 [LL15 23 N Kn I N1 METHOD FOR ALIGNING MECHANICALFILTERS The invention relates to a method for aligning mechanicalfilters. More particularly, the invention relates to a method foraligning mechanical filters in which the coupling of the individualfilter resonators is achieved via coupling elements comprising amaterial having a Youngs modulus which depends upon the temperature ofthe final heat treatment.

As is well known, mechanical filters consist of several mechanicalresonators which are mutually coupled to each other via one or morecoupling elements. The end resonators are usually designed aselectromechanical transducers for transforming electrical oscillationsinto mechanical vibrations or for transforming mechanical vibrationsinto electrical oscillations. A type of steel having a temperaturecoefficient of expansion as low as possible is usually utilized as theresonator material. A1- most any metallic material is suitable for useas the coupling elements. Generally, however, the same material isutilized for the coupling elements and the resonators.

Due to unavoidable manufacturing tolerances and structuralinhomogeneities occurring in the material of the coupling elements andthe resonators, a filter of the aforedescribed type does not immediatelyacquire the required transfer characteristic. It is therefore necessaryto suitably compensate for errors in material and manufacture. As iswell known, the process of compensation is known as the aligning of thefilter. In order to obtain the proper transmission characteristic, it isnot only essential that the resonant frequency of the individualresonators be at relatively exactly preset frequencies, but it is alsoimportant to adjust the degree of coupling to the correct value whichcomes as close as possible to the theoretical value. Although it ispossible to reduce the coupling, for example, by removing material fromthe coupling elements, the error which results from the removal of toomuch material cannot be reversed with any economically justified effort.

The principal object of the invention is to provide a method foraligning mechanical filters which particularly assures the correctadjustment of the coupling elements and with which, in particular, asubsequent increase of the coupling factor is possible.

An object of the invention is to provide a method for aligningmechanical filters which is automatic in order to assure an adjustmentprocess which is as efficient as possible.

An object of the invention is to provide a method for aligningmechanical filters which is simple in nature and functions withefficiency, effectiveness and reliability.

The method of the invention starts with a method for aligning mechanicalfilters in which the coupling of the individual filter resonators isaccomplished via coupling elements comprising a material having a Youngsmodulus depending upon the final temperature of the heat treatment. Inaccordance with the invention, the coupling elements are subjected to aheat treatment, the maximum temperature of which is higher than thefinal temperature of the heat treatment, or the precipitationtemperature.

It is particularly preferable, in accordance with the invention, tocarry out the heat treatment in a manner whereby the Youngs modulus ofthe coupling elements is increased.

In accordance with my invention, the material of the coupling elementspreferably comprises groups of materials which exhibit an anomaly oftheir Youngs modulus as a function of the temperature. Such groups ofmaterials are, for example, nickel-iron alloys, in which additions ofother, particularly metallic, materials are included. A suitablematerial of such type is known, for example, by the tradename Thermelastand is produced by the Vacuumschmelze Company of West Germany. As afunction of the final heat treatment temperature, which is also known asthe precipitation temperature, these materials have a Youngs moduluswhich initially increases with temperature and, after passing a maximummagnitude with increasing heat treatment temperature, decreases. Theindividual curves for the same material differ quantitatively only bythe degree of cold working to which the material was subjected prior tothe final thermal treatment.

In order that the invention may be readily carried into effect, it willnow be described with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram of the equivalent electrical circuit of acoupling element of a mechanical filter;,

FIG. 2 is a graphical presentation of the dependence of the Young'smodulus of Thermelast on the temperature, the parameter of the curvesbeing the degree of cold working of the Thermelast;

FIG. 3 is a graphical presentation of the relative variation of theYoungs modulus of Thermelast referred to an original final temperatureof heat treatment of 400C;

FIG. 4 is a schematic diagram and circuit diagram of an embodiment ofapparatus for localized heating of a coupling element of a mechanicalfilter in accordance with the method of the invention; and

FIG. 5 is a schematic diagram illustrating another embodiment forheating a coupling element of a mechanical filter in accordance with themethod of the invention.

In accordance with the analogy of electromechanical force to current,the equivalent electrical circuit of a short coupling element, having alength which is less than M8 wavelength, when A is the wavelength of thematerial, may, as shown in FIG. 1, be represented by a 12' circuitcomprising capacitances C in the shunt arms and an inductance L in theseries arm. For a coupling element which provides longitudinalvibrations or oscillations, for example, having a length a, acrosssectional area F, a Youngs modulus E, a mass m and a normalizedfrequency (.0

L A aw /EF and C A m/Z Only the inductance L is important for themechanical coupling factor. For a variation AL of the inductanee L,

wherein AE is the variation of Youngs modulus.

In FIG. 2, the abscissa represents the temperature T in C and theordinate represents the Youngs modulus E of Thermelast. As shown in FIG.2, the Youngs modulus initially essentially increases with increasingtemperature and reaches its maximum at approximately 500 to 600C,depending upon the degree of cold working of the Thermelast. In FIG. 2,curve 1 represents Thermelast having a degree of cold working ofpercent, curve 2 represents Thermelast having a degree of cold workingof 31 percent and curve 3 represents Thermelast having a degree of coldworking of 50 percent.

In FIG. 3, the abscissa represents the temperature T in C and theordinate represents the relative change or variation of Youngs modulus,referred to at original final treatment temperature of 400C. That is,the magnitude may be read directly at the ordinate of FIG. 3. Curves l,2' and 3 of FIG. 3 are obtained from the curves 1,

v 2 and 3 of FIG. 2, and represent 0%, 31% and 50% degrees of coldworking of the Thermelast, as in FIG. 2.

As shown in FIG. 3, for an initial final heat treatment temperature of400C, a variation of Youngs modulus of up to 4% may be provided bysubsequent heat treatment, depending upon the degree of cold working, ifthe final heat treatment occurs at a temperature between 400 and 600C.In accordance with the aforedescribed equations, a variation of thecoupling may thus be provided in the same order of magnitude if thecoupling elements comprise a material having a Youngs modulus whichdepends upon the final heat treatment temperature. It is only necessarythat care be taken that the maximum temperature utilized for varying theYoungs modulus is higher than the initial final heat treatmenttemperature or precipitation temperature. This method is preferablyutilized if the coupling is to be increased. It is also applicable, asshown in FIG. 2, however, if the coupling is to be decreased, andespecially if the heat treatment occurs at a temperature at which themaximum of the variation of the Youngs modulus has already occurred.Since the variations or changes of the coupling provided by my methodare in the order of magnitude of 3 to 4 percent, a relatively accurateadjustment may be obtained even if the properties of the material andthe tolerances occurring during manufacture have relatively high values.

FIG. 4 is a schematic diagram of apparatus for providing the method ofthe invention. The apparatus of FIG. 4 heats the individual couplingelements by direct current. A mechanical filter is illustratedschematically in FIG. 4 and comprises a plurality of resonators 5, infront view, mutually coupled via a coupling element 6. The couplingelement 6 extends beyond the end resonators in order to indicate thatadditional resonators may be included in the filter.

In FIG. 4, the coupling factor between the first and second resonators5, running from left to right, is K The coupling factor between thesecond and third resonators 5, running from left to right, is K Thecoupling factor between the third and fourth resonators 5, running fromleft to right, is K If contact electrodes 7 are placed on the couplingelement 6 and are energized by a voltage source 8, said coupling elementis locally heated and only the coupling factor K is varied thereby.

The heat provided by the electrical current may be adjusted by asuitable control device 9 connected in series with a current-controlledresistor I0.'The method may be made automatic by, for example, providinga temperature sensor 11 at each area of the coupling element to beadjusted. The temperature sensor 11 may control the resistor 10 via asuitable control device 12 and electrical connecting leads 13 whichconnect said control device to said resistor.

Another arrangement for heat treating the coupling elements inaccordance with the method of the invention, is shown in FIG. 5. In theapparatus of FIG. 5, a light source 15 functions as the heat source. Thelight provided by the light source is of sufficient density andsufficiently high color temperature. The heat source 15 may also be alaser. If the heat source 15 is a light source, a focusing arrangement16 may be provided in order to provide localized heating of the couplingelement 6.

Thus, for example, as illustrated in FIG. 5, the coupling factor K isheated by a beam path 17 due to the focusing arrangement 16.

The control arrangement of FIG. 4 may be applied in an analogous mannerto the embodiment of FIG. 5 if, instead of the variation of the current,the light intensity or the duration of the light pulses such as, forexample, the laser pulses, is controlled. 5

As hereinbefore mentioned, the method of the invention is particularlyadvantageous if it is important to increase the coupling without havingto add material to the coupling element or coupler in the process.Furthermore, since the adjustment may be made on the completed filter,the result of the alignment may be directly followed in electronic curvetracers such as, for example, Oscilloscopes, thereby providing analignment to a predetermined filter curve. Since relatively greatvariations are attainable in the coupling factor, the tolerances to bepreset for the manufacture of the filter may be selected larger and theproperties of the material used for the couplers or coupling elementsmay vary within wider limits. Although the variation or change of theYoungs modulus is accompanied by a variation of the temperaturecoefficient of the material of the coupling element, such variation,which is in the order of one part in a thousand, is practicallyinsignificant with regard to the required accuracies.

The control device 12 of FIG. 4 may comprise any of a great number ofsuitable arrangements. In one suitable arrangement, for example, thecontrol device 12 is basically a very simple control device whichcontrols the flow of current and, thus, the temperature in the couplingwire, in a manner similar to a thermostat. The control device 12 maycomprise, for example, a bridge circuit having four arms, a first ofwhich has a fixed resistor, a second of which has a fixed resistor and athird of which has a variable resistor. The bridge is energized by aconstant voltage applied to the junction point of the first and secondarms and the junction point of the third and fourth arms. The fourth armof the bridge has a pair of terminals connected to the temperaturesensor 11, which may comprise, in the illustrated example, aheat-dependent resistor. The variable resistor of the third arm of thebridge may determine a desired temperature. A control voltage may bederived from 'the junction between the first and third arms of thebridge and the junction between the second and fourth arms of thebridge, and drives a motor, for example, for adjusting thecurrent-controlled resistor 10. In a similar manner, the regulation ofthe current heat may be manually effected via the regulating device 9.

The light intensity or duration of the light pulses of the light sourceof FIG. 5 may be controlled in a similar manner.

While'the invention has been described by means of specific examples andin specific embodiments, I do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

1 claim:

1. A method for aligning a mechanical filter having individual filterresonators coupled to each other by coupling elements formed of materialhaving a Youngs modulus dependent upon the temperature of a final heattreatment to which the material has been subjected, which comprisesfurther heat treating the coupling elements to a maximum temperaturewhich is higher than the final heat treatment temperature so as tochange the Young's modulus of the material.

2. A method as claimed in claim 1, wherein the coupling elements areheat treated in a manner whereby the Youngs modulus is increased.

3. A method as claimed in claim 1, wherein the coupling elements areindividually heat treated by direct current heating.

4. A method as claimed in claim 1, wherein the coupling elements areindividually heat treated by radiations of a light source.

5. A method as claimed in claim 1, wherein the coupling elements areindividually heat treated by radiations of a laser.

2. A method as claimed in claim 1, wherein the coupling elements areheat treated in a manner whereby the Young''s modulus is increased.
 3. Amethod as claimed in claim 1, wherein the coupling elements areindividually heat treated by direct current heating.
 4. A method asclaimed in claim 1, wherein the coupling elements are individually heattreated by radiations of a light source.
 5. A method as claimed in claim1, wherein the coupling elements are individually heat treated byradiations of a laser.